DO NOW…. HW = 1 st formal prelab due tomorrow Which liquid has the highest density? Coussement, DeSchepper, et al., Brain Strains Power Puzzles  2002, page 16 least dense 1 < 3 < 5 < 2 < 4 most dense

Write out the three forms of the density equation. What are the most common units of density? M = DV D = M VM V V = M DM D D M V ensity ass olume

Density Practice Problems 3.A sample of iron has a mass of 94 g and a density of 7.8 g/cm 3. What is the volume of the iron? 94 g 7.8 g. cm 3 12 cm 3 V = M DM D

The density of lead is 11,340 kg/m 3. Find the density of lead in g/cm 3 11,340 kg 1000 g 1 m 1 m 1 m = m 3 1 kg 100 cm 100 cm 100 cm g cm 3

The average concentration of testosterone in the blood of a male in his twenties is 550 nanograms per deciliter. How many grams per cubic centimeter does this concentration represent? 550 ng 1 g 10 dL 1 L 1 mL = dL 1 x 10 9 ng 1 L 1000 mL 1 cm x g cm 3 C 19 H 28 O 2

A thimbleful of a neutron star would have a mass of over 90,718Mg. What is this mass in grams? 90,781 Mg 1 x 10 6 g = 1 Mg x g

Density of Some Common Substances Density of Some Common Substance Substance Density (g / cm 3 ) Air * Lithium 0.53 Ice Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3 Density of Some Common Substance Substance Density (g / cm 3 ) Air * Lithium 0.53 Ice Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3 *at 0 o C and 1 atm pressure

Consider Equal Masses Equal masses… …but unequal volumes. The object with the larger volume (aluminum cube) has the density. aluminum gold Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 71 smaller Christopherson Scales Made in Normal, Illinois USA

Density Practice Problems 1.What is the density of carbon dioxide gas if g occupies a volume of 100. mL? g 100. mL 1.96 x g/mL D = M VM V

Density Practice Problems 2.An irregularly shaped stone has a volume of 5.0 mL. The density of the stone is 1.75 g/mL. What is the mass of this stone? 1.75 g/mL x 5.0 mL 8.8 g M = D x V

Comparing Densities (g/cm 3 ) Jaffe, New World of Chemistry, 1955, page water 1.0 ice cork aluminum 2.7

INTENSIVEproperty Density is an INTENSIVE property of matter. - does NOT depend on quantity of matter. -Examples: color, melting point, boiling point, odor, density DIFFERENT THAN EXTENSIVE properties - depends on quantity of matter. - mass, volume, length Styrofoam Brick Gold

SI Prefixes (M) mega-1,000,000 (k) kilo-1,000 (d) deci- 1 / 10 (c) centi- 1 / 100 (m) milli- 1 / 1,000 (µ) micro- 1 / 1,000,000 Be sure to review how to use the example column on your Prefix Reference Sheet! Also know… 1 mL = 1 cm 3

Practice Measuring 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7 th Edition, page 7 cm

mL ? 15.0 mL

Scientific Notation  Calculating with scientific notation (5.44 × 10 7 g) = ?? (8.1 × 10 4 mol) 5.44 EE ÷ ÷ 78.1 = = 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator: Courtesy Christy Johannesson EE = = 4

Scientific Notation  Converting into scientific notation:  Move decimal until there’s 1 digit to its left. Places moved = exponent.  Large # (>1)  positive exponent Small # (<1)  negative exponent  Only include sig. figs. 65,000 kg  6.5 × 10 4 kg Courtesy Christy Johannesson

Scientific Notation 2,400,000  g kg 7  km 6.2  10 4 mm Practice Problems 2.4  10 6  g 2.56  kg km 62,000 mm Courtesy Christy Johannesson

Significant figures: Rules for zeros Leading zeros are not significant. Captive zeros are significant. Trailing zeros are significant, only IF there is a decimal point somewhere in the number. Leading zero Captive zero Trailing zero – three significant figures – four significant figures – five significant figures 11,420 – four significant figures

Other Ways of Thinking About Significant Figures…  All digits are significant EXCEPT…  Leading zeros  Trailing zeros without a decimal point -- 2,500  Pacific Ocean = “Present” and Atlantic Ocean = “Absent” (ask about this one in class ) Courtesy Christy Johannesson

Significant Figures  Calculating with Sig Figs (con’t)  Exact Numbers do not limit the # of sig figs in the answer.  Counting numbers: 12 students  Exact conversions: 1 m = 100 cm Courtesy Christy Johannesson

Significant Figures  Calculating with Sig Figs  Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = g 324 g 4 SF 3 SF Courtesy Christy Johannesson

Significant Figures  Calculating with Sig Figs  Add/Subtract - The # with the fewest places after the decimal point determines the # of sig figs in the answer. Courtesy Christy Johannesson g g  18.1 g g

Significant Figures (15.30 g) ÷ (6.4 mL) Practice Problems = g/mL  18.1 g 18.9g g g 4 SF2 SF  2.4 g/mL 2 SF Courtesy Christy Johannesson